This study is aimed at providing a more specific definition of the mechanisms underlying sudden cardiac death and myocardial infarction. In addition to identifying the sites and stages of infarctions, thromboses and the extent of obstruction by standard methods, special histopathologic techniques are applied to determine evidence of non-infarction myocardial injury as possible sources of ventricular arrhythmias and the nature of acute and subacute lesions of the coronary vessels. Retrospective case selection stresses but is not limited to moderate atherosclerotic and non-atherosclerotic heart disease ending in sudden death. The types and time of occurrences of clinical manifestations during the onset and pre-onset periods is obtained. A systematic analysis of the data is applied to determine the levels of association that exist among the clinical and pathologic findings.